1. Field of the Invention
The present invention relates to translating apparatus for an optical pickup device applicable to optical disc players such as an optical video disc player or the like and, more particularly, to a mechanism that translates an optical pickup device in the inner or outer diametrical direction of an optical disc, i.e.., a so-called rack and pinion system translating apparatus for an optical pickup device.
2. Description of the Related Art
Conventional optical pickup devices used in an optical video disc player, for example, operate to radiate a laser beam on a signal recording surface of an optical disc that is rotated at high speed. Then, the radiated laser beam that has been reflected on the optical disc is detected by a photodetector to thereby optically read out an information recorded on the signal recording surface of the optical disc. The information thus read out from the signal recording surface of the optical disc is converted into an electrical signal and thereby reproduced as an image or sound. The above optical pickup device is usually translated in the diametrical direction of the optical disc while the laser beam from the optical pickup device is tracing the tracks on the signal recording surface of the optical disc.
A swing arm system, a rack and pinion system, a belt drive system or linear motor system are known as a method of translating the optical pickup device in the diametrical direction of the optical disc. Of these systems, according to the translating method of the rack and pinion system, a rack is provided on the optical pickup device side and the rack is geared and moved by a pinion (drive gear) that is rotated by a feed motor in a decelerated fashion, whereby the optical pickup device is translated in the diametrical direction of the optical disc (see Japanese Published Utility Model Publication No. 2-29573, Japanese Laid-Open Utility Model Publication No. 58-62486, etc.).
However, the conventional optical pickup device translating apparatus of the rack and pinion system has a defect such that the optical pickup device is translated at high speed, i.e., the optical pickup device is recklessly translated by the feed motor to which an overcurrent is applied due to the influence of an electric circuit or the like in a drive system, for example, during the time translating apparatus is in adjustment. If the optical pickup device is translated recklessly, then the optical pickup device hits the chassis side at the innermost or outermost peripheral position of the optical disc so that the rack or pinion is damaged by an impulsive force applied thereto.
In order to protect the rack or pinion from being damaged, it has long been customary to avoid the impulsive force of the optical pickup device by using a shock absorbing material. However, if an impulsive force is beyond a certain limit, then the shock absorbing action of the shock absorbing material becomes ineffective, which unavoidably causes the rack or pinion to be damaged.
As another proposal for protecting the rack or pinion from being damaged, it has been customary to change the material of the rack or pinion or to enlarge the size of assembly parts so that the rack or pinion can endure the impulsive force. In this case, there is a limit in strength. Further, in a motor using a worm as an output shaft, when the optical pickup device is shocked, a worm and a worm wheel are locked so that an inverting operation of the driving system is disabled.
On the other hand, in the optical pickup device translating method of the belt transport system, the impulsive force of the optical pickup device is transmitted to the belt itself so that the belt is deteriorated earlier because the belt is extended. Also, assembly members such as a pulley or the like are needed in association with the belt, which increases the number of assembly parts.